1. Field of the Invention
This invention relates to a process for forming a cellulosic, non-binding pulp useful in making high bulk, high porosity, fibrous cellulosic substrates which comprises contacting the pulp with a non-oxidative gaseous medium. This invention also relates to novel non-alpha cellulosic pulps and substrates made therefrom which comprise at least about 10% hemicellulose.
2. Description of the Prior Art
The treatment of cellulosic substrates, i.e., paper, with such non-oxidizing heat transfer mediums as steam is well known to the prior art. Such treatments have been employed to accomplish a number of objectives. For example, U.S. Pat. No. 2,760,410 discloses the removal of liquid water from a newly formed paper substrate by contacting therewith superheated steam. Compare U.S. Pat. Nos. 2,590,849 and 2,590,850 which make use of the latent heat of steam by employing saturated steam for the removal of water or solvents from a paper substrate. The steam employed therein is generally at relatively low temperatures, e.g., of about 150.degree. C. (302.degree. F.). Saturated steam has also been used to reduce the hygroscopicity of regenerated cellulose staple fibers. See U.S. Pat. Nos. 2,608,460 and 1,544,885. The treatment of cellulosic pulps, e.g., wood pulps, with a non-oxidizing gaseous medium such as steam, however, has heretofore not been known to the prior art.
Mercerization is a treatment to which cellulosic pulps such as wood pulps are frequently subjected. Chemical mercerization of a cellulosic pulp is a well known process for producing alpha pulps, i.e., pulps having an alpha cellulose content of greater than 90%. The alpha pulps obtained form high bulk and highly porous cellulose substrates which are useful as filtering media, as is well known in the art.
The economic attractiveness of the chemical mercerization process, however, which generally involves contacting a cellulosic pulp with an 18-20% caustic solution, such as sodium hydroxide, in order to dissolve the beta and gamma cellulose and leave the non-soluble alpha cellulose, is somewhat dubious due to the cost of the chemicals employed and the safeguards in the handling thereof. All of these costs add to the high cost of the final product. Moreover, there is also a loss in yield of the pulp when employing the mercerization process due to the dissolution of the beta and gamma cellulose.
Accordingly, it is an object of the present invention to provide a low-cost process for forming a cellulosic pulp suitable for making a high bulk, highly porous cellulosic substrate.
Another object of the present invention is to provide a novel cellulosic pulp containing at least about 10% hemicellulose which is suitable for forming a novel cellulosic substrate also containing at least 10% hemicellulose.
A further object of this invention is to provide a process for preparing a cellulosic pulp suitable for forming a high bulk, highly porous cellulosic substrate without experiencing a loss in yield of the pulp.
Still a further object of the present invention is to provide a process for preparing a cellulosic pulp suitable for forming a high bulk, highly porous cellulosic substrate without the use of chemicals.
Another object of the present invention is to provide a safe process for thermally treating a cellulosic pulp which requires a short residence time and avoids oxidative damage to the cellulosic fibers.
Other objects, features and the advantages of this invention will become apparent to those skilled in the art upon a study of this disclosure, the appended claims, and the drawing.